There is a general desire in all technical fields to be energy efficient. In the building industry, for example, there is a permanent need to decrease the energy costs related to heating and cooling indoor rooms. The same applies also in the textile industry, for instance for life and personal protection clothing, where the heat excess produced by the wearer must be removed and managed away from his body in order to increase the overall wear comfort.
PCM materials are highly-productive thermal storage media which are capable of absorbing and releasing high amounts of latent heat during melting and crystallization, respectively. During such phase changes, the temperature of the PCM materials remains nearly constant and so does the space surrounding the PCMs, the heat flowing through the PCM being “entrapped” within the PCM itself. Paraffin waxes are known to be particularly efficient as PCMs.
FIG. 1 shows a temperature profile simulation of the inside surface of three building wall structures (wood timber frames) during a typical summer day (latitude 45°; azimuth 180°; air Tmin 15° C.; air Tmax 35° C.). Such three wall structures comprise an external layer (wood siding, thickness 20 mm), a stone wool layer (thickness 250 mm) adjacent to such external layer and an internal gypsum board (thickness 10 mm). The first wall structure (W1) does not include PCM, while the second and third wall structures (W2,W3) further comprise a PCM composition layer positioned between the stone wool layer and the gypsum board layer, the PCM composition layers consisting of 7.15 wt % of PCM and 92.85 wt % of an hypothetical polymer and 45 wt % of PCM and 55 wt % of an hypothetical polymer, respectively. The PCM considered for this simulation is commercially available from Rubitherm under the trade name Rubitherm® RT20 (melting point 22° C.).
FIG. 1 shows that the variation of the inside wall temperature during the day is reduced with increasing PCM amount in the wall structure or, in other words, that the heat management performance of the wall structure increases with increasing amount of PCM included therein.
WO 2004/044345 discloses a wall covering assembly comprising phase change materials like crystalline alkyl hydrocarbons as a thermal storage mean. The assembly comprises 1) a cover layer of fabric or paper covered by a vinyl coating; 2) an intermediate layer made of an acrylic coating compound which contains finely divided PCM and a rear layer made of a liquid ceramic compound facing the wall during use. However, the capacity of the acrylic coating to incorporate PCM is limited due to the polarity and the elevated crystallinity degree of the acrylic material itself, so that the heat storage capacity of the overall assembly is limited to a certain extent.
U.S. Pat. No. 5,053,446 discloses a composite useful in thermal energy storage, said composite being a polyolefin matrix having a PCM (for example a crystalline alkyl hydrocarbon) incorporated therein. The polyolefin matrix is crystalline and must be thermally form stable up to temperatures of 150-180° C. This is due to the fact that the PCM imbibition of the matrix must take place at temperatures up to the above values in order to enable the PCM material itself to penetrate into the narrow spaces of the crystalline matrix. The thermal stability is usually achieved by reticulating the polyolefin prior to the imbibition process. This is an additional step for the preparation of the composite material, which additional step renders the overall manufacturing process more complicated and expensive. Furthermore, because of the limited space available within the matrix itself, proper retention of the PCM, particularly at temperatures below the PCM melting point, is very difficult, thus leading to a strong decrease in the heat management performance of the overall composite.
The problem at the root of the present invention is therefore to provide a PCM composition for the thermal management in different applications like for example in building, automotive, garments and footwear, which PCM composition can overcome the problems mentioned above.